C++ 如何与libpqxx API同时插入数据？（PostgreSQL，线程）

使用的材料：

库：

libpqxx:x64 windows版本6.4.4

操作系统：Windows 10

编译器：VisualC++（MSVC）

这是我的SQL表：

CREATE TABLE test(
    test_name VARCHAR(16)
);

这是我的简约测试版本：

main.cpp 如何与此API同时插入？

解决方案链接：

就我而言，我将连接更改为

static thread_local database_connection;

因此，每个线程都有自己的连接，代码工作时不会有太多变化。

解决方案链接：

就我而言，我将连接更改为

static thread_local database_connection;

---

因此，每个线程都有自己的连接，然后代码就可以正常工作，而不会有太多变化。

线程很困难。请确保正确同步访问。您不能。postgress连接实际上是单线程的。如果要并行插入，每个线程必须打开自己的连接并使用它来插入数据。线程很困难。请确保正确同步访问。您不能。postgress连接实际上是单线程的。如果要并行插入，每个线程必须打开自己的连接并使用它插入数据。

#include "test.h"
#include <iostream>
#include <pqxx/transaction.hxx>

test::test(pqxx::connection* database_connection) : database_connection(database_connection)
{
    for (auto& i : threads)
    {
        i = std::thread(&test::InsertData, this);
    }
}


void test::InsertData()
{

    pqxx::work work(*database_connection);
    try
    {

        pqxx::result result = work.exec_prepared("insert_into_table", "test_data"); //prepared data in real project pqxx::binarystring blobs

        work.commit();

    }
    catch (const std::exception& e) {
        work.abort();
    }

}

Exception thrown at 0x00007FFC2FF44008 in Project3.exe: Microsoft C++ exception : pqxx::usage_error at memory location 0x000000CEB00FF050.
Exception thrown at 0x00007FFC2FF44008 in Project3.exe: Microsoft C++ exception : pqxx::usage_error at memory location 0x000000CEB03FEF50.
Exception thrown at 0x00007FFC2FF44008 in Project3.exe: Microsoft C++ exception : pqxx::usage_error at memory location 0x000000CEB04FED30.
Exception thrown at 0x00007FFC2FF44008 in Project3.exe: Microsoft C++ exception : pqxx::usage_error at memory location 0x000000CEB02FEAF0.
Debug Error!

Approaches for thread - safe programs

Approach 1: single database thread
Make one of your threads the dedicated "database thread." Ensure that that thread is the only one that ever accesses objects or functions from libpqxx.Use message - passing to channel all your database interactions through this thread.

This approach should be safe even if your libpq build is not thread - safe.

Approach 2 : global lock
Let multiple threads access objects and functions from libpqxx, but never simultaneously.Use a single, global lock to protect any access to libpqxx.

You do need a lock of some sort.You can't generally rely on other ways to know that thread 1 is done before thread 2 uses the library! Data from thread 1 may still be cached in a register or, depending on your system architecture, a processor cache that thread 2 isn't synchronized with.Or vice versa.It gets ugly and subtle.

Approach 3 : thread - local connections
Every connection in libpqxx acts as its own little world.It produces result objects, you create transactions on it, it uses error message callbacksand so forth.Keep all of the objects related to a connection exclusively inside the same thread that created the connection.This way you'll need no locking at all.

Of course you can still have more than one connection inside the same thread.This model should be fine for most applications, so this is probably as far as you'll want to read.

Approach 4 : per - connection locking
If you really have to share any libpqxx objects at all between threads, set up one lock per connection.This lock should protect all objects related to that connection.That way, all access to a connectionand its related objects will be serialized as if they all stayed in the same thread.

The risk of deadlocks may be slightly greater if you go this way.

static thread_local database_connection;